The present invention relates to ion exchange materials.
Ion exchange materials have been used for purification and demineralization. These materials have a three-dimensional network to which ions are attached. In ion exchange resins, the three-dimensional network is a polymer. In carbon ion exchangers, the three-dimensional network is activated carbon.
Carbon ion exchangers may be prepared in a variety of forms, including, for example, fibers. These carbon fiber ion exchangers are described in xe2x80x9cTailoring Carbon Fibers for Adsorbing Volatilesxe2x80x9d Economy, James, et al.CHEMTECH (1992), 22(10), 597-603.; xe2x80x9cProperties of Sorption-Active Carbon Fibersxe2x80x9d section 3.6 of Chemically Modified Carbon Fibers and Their Applications, Ermolenko, I. N., et al., translated by Titovets, E. P., VCH Publishers, Inc., New York, 1990.; and xe2x80x9cSurface Modification of Carbon Fibersxe2x80x9d Chapter 6 of Chemically Modified Carbon Fibers and Their Applications, Ermolenko, I. N., et al., translated by Titovets, E. P., VCH Publishers, Inc., New York, 1990. The material may be prepared by first making activated carbon fibers (ACFs), and then introducing ionic groups into the ACFs by chemical reaction with modifying agents, such as, for example, sulfonation with concentrated sulfuric acid, or phosphorylation with phosphorus trichloride.
Carbon fiber ion exchangers that contain strongly acidic groups, such as sulfonic groups, are of particular interest, because of the ability of these materials to remove difficult to coordinate ions, such as Cs+. These ions may be present as radioactive ions in contaminated water. The capacity of an ion exchanger to remove these ions can be determined by measuring the capacity of the ion exchanger at low pH, such as at a pH of 1. It would be desirable to have carbon fiber ion exchangers with greater capacity at low pH.
Since carbon fiber ion exchangers are typically made from ACFs, they suffer from some of the same disadvantages. For example, extreme weight loss results during the production of ACFs, limiting their cost-effectiveness. Furthermore, ACFs are usually brittle or frangible, due to producing these fibers by carbonization at high temperatures; these poor mechanical properties limit their utility to systems containing some sort of mechanical support, and make it difficult or expensive to produce forms such as woven fabrics, felts and papers.
Glass or mineral fibers, coated with activated carbon, have been prepared. These materials are described in U.S. Pat. No. 5,834,114. Glass or mineral fibers coated with activated carbon are described as being prepared by coating a glass or mineral fiber substrate with a resin, cross-linking the resin, heating the coated fiber substrate and resin to carbonize the resin, and exposing the coated fiber substrate to an etchant to activate the coated fiber substrate.
In a first aspect, the invention includes a composite, containing (i) substrate fibers, and (ii) carbon ion exchanger, on the substrate fibers.
In a second aspect, the invention includes a method of making a composite, including introducing ionic groups into an activated coating, to form a carbon ion exchanger. The activated coating is on substrate fibers.
The term xe2x80x9ccarbon ion exchangerxe2x80x9d means an ion exchange material made from an activated coating.
The term xe2x80x9cactivated coatingxe2x80x9d means a material that contains carbon and has a B.E.T. surface area of at least 50 m2/g. This term includes activated carbon.
The term xe2x80x9ccarbon fiber ion exchangerxe2x80x9d means an ion exchange material made from an activated carbon fiber.
The term xe2x80x9ccarbon ion exchanger composite fiberxe2x80x9d means an ion exchange material made from an activated coating, that is present on a fiber.
The term xe2x80x9cion exchange materialxe2x80x9d means ion exchange materials as well as materials that contain groups capable of chelating ions.